A conventional pedaling training machine has a kind of brake adjuster which comprises a belt to be gradually tightened around a turning disc to obtain effect of stopping the machine. Another kind of brake adjuster comprises an iron turning disc interposed between two permanent magnets of different polarity and the dimension of the turning disc facing the permanent magnets is to be adjusted to obtain different extend of force for stopping the training machine.
The latter can reduce very much wear and tear of components because of no friction between them, but the permanent magnets can be pulled up by fast rotation of the turning iron disc, which is positioned at a constant location. And the permanent magnets are originally positioned to vertically cross the iron turning disc, but the iron turning disc is turning very fast, and magnetic pulling force generated by the permanent magnets can allow the magnets to be pulled up gradually by inertia of the turning disc to incline up against the disc so that the dimension of the magnets facing the disc gradually decreases. And the larger the pedaling force is, the more the magnets can be inclined up. Then the brake loses its stopping force in proportion to the bias angle of the magnets.